Dynamometer testing of vehicles is known per se, and can, for example, be carried out by roller type dynamometers equipped with large rollers that support the vehicle wheels, and which are used to apply a brake torque to the drive wheels of the vehicle. Such systems, however, are not always capable of providing the desired measurement accuracy and/or measurement freedom.
Another kind of vehicle dynamometers for dynamometer testing of vehicles is disclosed in U.S. Pat. No. 4,669,318 (Ångström). This document relates to an apparatus for dynamometer testing of vehicles, where load absorbing means in the form of a hydrostatic pump assembly has an input shaft for engagement with a drive shaft of a vehicle to be tested. Each drive shaft is fixedly connected to an individual apparatus of this kind, whereby a total effective torque from the vehicle can be accurately measured.
Systems of the kind disclosed in U.S. Pat. No. 4,669,318 are reliable, and are capable of accurately measuring torque in steady load situations.
It is also possible to perform more complex tests using a dynamometer testing system of the above kind, both for two-wheel drive systems, and also for four-wheel drive systems. Such more complex testing, using a system of the above kind, is disclosed in the International patent application WO2007/133154 A1 (Engstroem).
However, vehicle transmissions are becoming increasingly complex, and there is also an increasing desire to perform measurements that allows accurate measurement of various vehicle characteristics taking into account numerous situations that may occur during real life driving of the vehicle on a road.
Aim and Most Important Features of the Invention
It is an object of this invention to provide an improved system for dynamometer testing of vehicles.
According to the present invention, it is provided a dynamometer test unit for dynamometer testing of a vehicle, where the vehicle includes at least a first wheel shaft and at least one first vehicle power source for providing power to said first wheel shaft. Said first wheel shaft is, during testing, connected to said dynamometer test unit, said dynamometer test unit including:                a first individually controllable dynamometer power source for applying a first power to said first wheel shaft,        a second individually controllable dynamometer power source for applying a second power to said first wheel shaft, wherein        during testing, said first and said second dynamometer power source apply a controllable power to said first wheel shaft.        
The present invention has the advantage that use of dynamometer test units having two (or more) power sources allow, at least in some situations, more accurate dynamometer testing of vehicles.
In particular, the present invention is advantageous for testing of vehicles where power can selectively be applied from two (or more) separate vehicle power sources to the same wheel shaft of a vehicle e.g. to absorb a controllable power from said first wheel shaft.
For example, one of the vehicle power sources can be of a kind capable of delivering high torques at low speeds, such as e.g. a low power electric motor, while another vehicle power source being capable of providing high power at high speeds, such as e.g. higher power electric motor or combustion engine.
Use of two or more controllable dynamometer power sources (that is, power sources that repeatedly can be set to substantially desired and defined torque/power/rotational speed using direct control, i.e. by calculating a control signal by means of one or more mathematical representations of the dynamometer power source), e.g., has the advantage that the dynamometer power sources can be designed to absorb power from such vehicle power sources in a favourable manner, since use of plural dynamometer power sources connected to a single vehicle wheel shaft has the advantage that the dynamometer power sources can be designed with very varying torque absorbing characteristics.
For example, the present invention can be used for accurate testing of vehicles having hybrid drive trains, and the vehicle, e.g., can include two or more power sources acting on the same wheel shaft. Use of a dynamometer test unit according to the present invention has the advantage that the different characteristics, e.g. with regard to torque/rotational speed characteristics, that such vehicle power sources can give rise to can be accounted for.
This has the further advantage that a dynamometer test unit having two (or more) dynamometer power sources with different torque-speed characteristics allows dynamometer test units of considerably more favourable design with respect to cost/space/infrastructure requirements than would be the case with a single power source having the total capability of the two dynamometer power sources taken together.
For example, at least one of said first and second dynamometer power sources can be an electric motor. Alternatively or in addition, at least one of said first and second dynamometer power sources can be a hydraulic pump.
The present invention, thereby, provides a solution that is capable of accurately testing driving situations that can arise using sophisticated vehicle drive trains.
According to one embodiment of the invention, the dynamometer test unit includes two power sources, where at least one of said dynamometer test unit power sources is capable of providing a negative (braking) power to said wheel shaft, and one power source is capable of (at least) applying a positive (motoring) power to said wheel shaft.
This has the advantage that the present invention can be used also for testing of vehicles having means for regenerative braking, e.g. hybrid drive vehicles having a power source in the form of an electric motor. One dynamometer power source can then be used to propel the vehicle wheel shaft, so that e.g. a vehicle electric motor can be used for braking purposes, e.g., in order to simulate deceleration of the vehicle, and act as a generator instead of as a motor to regenerate electrical energy for feed-back to e.g. an energy storage.
The use of dynamometer test units being capable of providing both a negative (braking) and positive (motoring) power to a wheel shaft allows that e.g. a hybrid drive vehicle can be tested not only for accelerations, but also for complete test drives, with uphill as well as downhill driving.
Further, with regard to power being absorbed by dynamometer test units, power sources that absorb power in a way that allows intermediate storage and transportation can be used. For example, absorbed power can be converted either to electricity or hydraulic pressure. The absorbed and converted power can then be transported away from the immediate vicinity of the wheel shaft, so as to avoid problems with excessive heating at the location of power absorption.
Consequently, according to the present invention kinetic energy can be absorbed from the vehicle wheel shaft without direct conversion of at least a majority of the absorbed power to heat.
As is exemplified in the following detailed description of the present invention, there also exist numerous other situations where the present invention can be utilized.